1. Field of the Invention
The present invention relates to plasticizers, known generally as polymeric plasticizers, which are derived from certain polyesters. The present invention further relates to the use of such plasticizers in the formulation of polymeric compositions, particularly compositions based on polyvinyl chloride polymers, and to such compositions.
2. Background of the Invention
Plasticizers in general are a well-known type of chemical constituent useful in the formulation of polymeric compositions. They perform useful functions including imparting flexibility, processability and the like to the polymer composition compared to the properties that would be exhibited by the same composition in the absence of the plasticizer component.
So-called polymeric plasticizers have been described in the past which, in addition to the plasticizing properties they impart, are believed to exhibit additional useful properties such as low volatility; low extractability from the polymer into water, soap and detergent solutions, organic solvents, oil, and the like; and minimal migration from the polymer matrix into other materials which come into contact with the polymer containing the polymeric plasticizer. For instance, refrigerator gaskets need to be flexible at room temperature and lower temperatures, and thus require fabrication with a plasticizer component, yet such gaskets can come into contact with adjacent refrigerator parts made of e.g. polystyrene. Migration of the plasticizer component from the gasket into the polystyrene could result in unsightly roughening and frosting of the polystyrene surface (conventionally called "marring"), and the loss of plasticizer from the gasket can in time lead to an undesirable loss of flexibility of the gasket. Appropriately chosen plasticizers, such as in particular polymeric plasticizers, reduce or eliminate this problem.
In general, the desirable properties associated with polymeric plasticizers tend to be exhibited to a greater degree with increasing molecular weight of the plasticizer. However, increased molecular weight of the plasticizer can tend to increase other properties such as the viscosity of the material and the processing time required in compounding the plasticizer component into the polymer. In addition, increased molecular weight tends to decrease the plasticizing efficiency, that is, a greater weight concentration of the plasticizer is required to accomplish a given degree of plasticization of the polymer (as measured, for instance, by hardness or tensile properties).
Thus, there remains a need for polymeric plasticizers which exhibit an optimum combination of plasticization and the associated desirable properties such as low extractability, migration, and the like, while minimizing the less desirable properties such as lessened efficiency and more difficult processing.
3. Description of the Prior Art
The prior art has recognized polymeric plasticizers but has not disclosed or suggested the particular plasticizers of the present invention and the desirable combination of properties afforded thereby.
For instance, published Japanese Patent Application No. 59(1984)-202,181 (Kokai No. 61(1986)-78,827) discloses polyester plasticizers of the general formula L--G(--D--G).sub.n --L in which L is the residue of a monobasic acid said to contain 2 to 22 carbon atoms, G is the residue of 2-methyl-1,3-propanediol, D is the residue of a dibasic acid such as azelaic acid, sebacic acid, or an aromatic dibasic acid such as phthalic acid, isophthalic acid, terephthalic acid, and their anhydrides, or an alicyclic dibasic acid such as cyclohexane dicarboxylic acid. While this publication recognizes in general virtues of a plasticizer containing a 2-methyl-1,3-propanediol based polyester it does not suggest the particular structure of the polymeric plasticizers which are the subject of the present invention.
U.S. Pat. No. 5,281,647 also discloses polymeric plasticizers derived from polyesters, wherein the polyester is derived from a diacid containing 5 to 13 carbon atoms and a highly hindered diol, that is, a diol exhibiting a highly branched structure. This patent also does not recognize the particular structure of the polymeric plasticizers which are the subject of the present invention.